I want to know what interactions I'll miss by having started a fresh game.

Assuming everyone survived, where do they appear and what importance does everyone's cameo have?

I'm looking for a complete list of Mass Effect 2 squadmates and description of their interactions with Shepard in Mass Effect 3.

What I have in mind is something like this:

Legion
- Can be found in mission X standing next to the barrel on the right of the first room.
- If talked to, he tells Shepard of how he freed his kind from a slave camp.
- Can be recruited to tag along.

1 Answer
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Kaidan or Ash shows up at the end of the first mission. They will be unavailable to the party for a while. They can possibly die, or re-join the party later on.

Liara joins the party on Mars.

Garrus shows up when you go to rescue the Turian leader and joins
your party

Kasumi shows up when you agree to help a fellow Specter investigate a Hanar diplomat on the Citadel. When the mission ends, she can join up as a war asset.

Thane is in the hospital on the Citadel. He cannot join your mission since his condition is terminal.

Miranda will communicate with you several times, and meet up on the citadel. You will later encounter her on a mission where it is possible for her to die. If she survives she will become a war asset.

Zaeed can be found on the Citadel while investigating the Volus
ambassador. This quest is triggered after the Cerberus attack on the
Citadel. He can join up as a war asset.

Wrex, shows up at the summit between the alien leaders after you
retrieve the Turian patriarch. He stays on the Normandy, but he does
not join your party.

Mordin can be found on the mission to rescue the Krogan Females. He
will come aboard the Normandy, but he won't join your party.

Grunt is found on a mission from Wrex to rescue some Krogan scouts.
He can join up as a war asset.

Jack shows up during the rescue mission to the Grissom Academy. She
may join up as a war asset, and you can later talk to her at the
night club on the Citadel.

Jacob is found in the mission to retrieve some Cerberus scientist
that is triggered after the attack on the Citadel. He can join up as
a war asset and can be talked to at the Hospital.

Samara is found in the mission to investigate an Asari colony that
is triggered after the attack on the Citadel. She can join up as a
war asset and can be talked on the Citadel

Tali and Legion are both found in the mission to recruit the Quarian
fleet. Tali can join your team, but what happens to Legion is very
dependent on player choice.

During the end game you will have the opportunity to speak with all
your surviving squad mates past and present one last time.

Some other Normandy crew non-squad mates show up as well.

Dr. Chakwas can be found in the Citadel hospital and can re-join the
crew.

The two Normandy engineers from ME2 can be pardoned in the Spectre
office, and will rejoin the crew.

Kelly Chambers can be found in the refugee camp on the Citadel. She
won't join your crew. You should also convince her to go into hiding
or she'll get assassinated by Cerberus operatives when they attack
the Citadel. She can also be romanced.

At the end of the game you will be able to communicate with all of your surviving squad mates before the final mission.